The present invention relates to a machine and method for mechanically stripping the insulation from an insulated stator bar without damage to the copper strands of the bar, so that the bar can be reinsulated for use in a stator winding.
During the factory production of stator bars, occasionally a stator bar is rejected because the cross-sectional dimensions of the insulated bar are out of prescribed tolerance limits or because it fails at the electrical proof test. Occasionally, in generators in power plants, the stator bar insulation fails in service or during electrical tests, making the bar unsuitable for continued service. In these instances, the lead time required to manufacture a replacement bar starting from raw materials is long and is unacceptable for meeting the schedule for shipment of a new generator from the factory or for returning the generator to service. Accordingly, conventionally, the ground wall insulation from the rejected and/or failed bar is stripped down to the bare bar and the bar is reinsulated for assembly in the stator.
Conventionally, the insulation is stripped manually, using hand tools. This method is slow and has the potential for damaging the copper strands of the bar, rendering it unsuitable for reuse.
The present invention provides a machine and method for stripping the ground wall insulation from a stator bar quickly and in such a manner that the copper strands will not be damaged. The apparatus of the invention includes a power driven cutting tool for milling or routing the insulation from a portion of the insulated bar, a sensing device for detecting the location of the copper strands and a height adjustment assembly for determining a disposition of the bar with respect to the cutting tool. In an exemplary embodiment, the height adjustment assembly is adjusted in accordance with the location of the copper strands as detected by the sensing device to substantially prevent the cutting tool from making damaging contact with the copper strands.
In an exemplary embodiment, the machine or apparatus is mounted to an insulated stator bar to be stripped and is driven longitudinally of the stator bar to cut the insulation along the length of the stator bar.
Accordingly, the invention is embodied in a stator bar stripping machine for removing insulation from a portion of an insulated stator bar, that comprises a power driven tool, including a cutter for milling the insulation from a portion of the insulated stator bar; a housing for at least partly enclosing the power driven tool; a support assembly for supporting the housing with respect to the stator bar; a sensing device for detecting a location of copper strands of the stator bar; and an adjusting mechanism for adjusting a disposition of the housing with respect to the stator bar so as to adjust a cutting depth of the power driven tool into a surface of the stator bar.
In an alternate embodiment of the invention, first and second power driven cutting tools are provided for simultaneously cutting spaced portions of the insulating material to thereby facilitate removal of the insulation from the copper strands following a single pass with the machine.
The invention is further embodied in a method of stripping insulation from a stator bar that comprises providing an insulation stripping machine including a power driven tool generally as described above, mounting the stripping machine to a stator bar by receiving the stator bar into the housing; and actuating the power driven tool to mill insulation from a portion of the insulated stator bar.